This document contains several AGA documents that comment on the AGA rules . See also the Concise AGA Rules .
Fred Hansen
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AGA Rules Committee
April 1, 1991
For the sake of simplicity, start by assuming an even game, that both players play exactly the same number of stones, only passing at the end, and that at the end of the game there are no neutral points (all dame filled and no seki). Make the following definitions:
Now, we have the following relationships. Since we are assuming that both players have played exactly the same number of stones, we have:
This means that:
So, adding Tb - Tw to both sides,
If a player passes prior to the end of the game, it will reduce that player's area score by one point per pass relative to the corresponding territorial score. The convention of handing a "pass" stone to the opponent when passing keeps the two scores equal. (In general, it can only hurt a player to pass prior to the end of the game.)
There are also certain rare situations where a game ends with "one-sided dame" (see Figure 5) which one side can fill but the other cannot. Each additional stone played represents the gain of a point under area counting. But since the opponent will be forced to hand over a "pass" stone on his or her move, each additional stone played also represents the gain of a point under territory counting--the two remain equivalent!
Finally, in a handicap game, the additional points of compensation paid by Black to White can be thought of as "reverse pass stones" ensuring that both players have, in effect, still played exactly the same number of stones.
If we assume that the two players have played the same number of stones, with no neutral points left on the board, and that the score in equation [1] is equal to k, we have:
But
So k must be odd!
This implies that if such a game is even on the board by traditional territorial counting (without pass stones), Black must have made the last move! At one time, the Chinese rules compensated White with an extra point when Black got the last move. If Black's last move was to fill a ko he or she had won, however, it was deemed unfair to penalize him or her, so eventually the Chinese removed this proviso. Requiring that White always have the last move and using pass stones removes the possibility of a "pass fight" over who gets the very last move.
If there are neutral points on the board at the end of the game (presumably in seki, since the players would naturally fill all dame under the area system), the same argument still shows that the two systems give the same result if the players have played the same number of stones, but the parity of k will depend on the number of neutral points; if there are an odd number of neutral points, k will be even, and vice versa. This may explain why some rule systems go to great lengths to award all points in seki.
Finally, note that in the confirmation phase, by our rules, the final
result remains the same (that is, the "same" as would be calculated before
playing out the confirmation phase if the status of all groups were
taken to be whatever it proves to be through the confirmation process!)
Since the game is over, we can assume that all empty points belong
to the territory of one or the other of the players. Under area counting,
stones of either color played into one's own territory or into the
opponent's territory will not change the score--nor will the "pass" stones.
Under territorial counting, every stone played into one's own or the
opponent's territory will cost a point--but by requiring that the players
make the same number of moves, and by insuring that even passes cost
a point (the "pass" stones), we insure that the end result is still the
same.
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To: IGF Rules Committee
From: AGA Rules Committee
Date: April 1, 1991
Re: Rules Proposals
The 1990 Intemational Go Federation Rules Committee meeting took a significant step in agreeing in principle, at the initiative of the Japanese representative, to sanction multiple sets of rules for use in international amateur play.
As the Committee knows from our previous presentations, the American Go Association has for several years been working toward a "simplified" set of rules for use among amateurs--a set of rules at once simple enough to be understood by beginners, clear and comprehensive enough to guide tournament play among amateurs--when the tournament director (and the strongest players present) may not even be of dan level--and acceptable to players from all cultural backgrounds.
Our Rules Committee has now adopted a proposed set of AGA Official Rules of Go which we believe meets these criteria. These rules are similar to those we presented at the 1990 IGF Rules Committee meeting, but have benefitted greatly from the discussions we took part in there, both in committee and with individual participants, and from further discussions with interested parties in the Canadian Go Association, the New Zealand Go Association, and various European Go Associations.
Super-Ko: A super-ko rule prohibiting full board repetitions is adopted. This covers all potential repetitive situations in one stroke, and guarantees that every game must have a definite outcome. Situations involving multiple kos and/or other potentially infinite repititions are rare. When they do arise, the care required to avoid a full-board repetition is not so much greater than that required in handling ordinary multi-step or multi-stage kos, and seems to form a natural strategic component to the game. Most importantly, it is clear in principle even to beginners how every such situation is handled. We believe this approach is preferable to handling such potential repetitions on a case-by-case basis, or causing a game to be annulled.
Use of Pass Stones: Our rules provide that the players must make an equal number of moves during the game, and that when a player passes, he or she must pass the opponent a "pass" stone (previously referred to as a "bookkeeping" stone), which is treated like any other prisoner. The requirement that the players make an equal number of moves (i.e., that in an even game White must make the last move) serves to guarantee that passing is never beneficial before the end of the game. (Without this proviso, one can have situations where the players get into rather strange "pass fights" over who gets the very last move, as James Davies has pointed out.) The use of pass stones keeps the actual number of stones played (or exchanged) equal, and thus guarantees that area and territory counting give the same result. Finally, offering a pass stone to the opponent provides a neat "language free" method for proposing an end to the game!
Settling Disputed Status of Groups: The status of disputed groups is to be settled by playing out the full-board situation.
Playing out the situation allows players of varying levels to resolve complex life-and-death situations according to their abilities, without depending on outside authorities or exhaustive analysis, and hence is most suitable for amateur play. While the new Nihon Ki-in rules are carefully crafted to resolve most of the difficult cases which used to require exccptional handling, and are probably very appropriate for professional play, they depend on a high level of sophistication in analyzing each position based on rules which are slightly different from normal play (due to the special handling of kos). In principle, resolving such end-of-game disputes requires the players--or some competent authority in attendance--to have the capacity to resolve life-and-death problems of arbitrary complexity! Rather than attempt to resolve each local situation "in principle" in the ideal fashion through extensive analysis, playing the position out achieves a fair result (it is based on the relative reading strengths of the players themselves) in potentially bounded time without the need to appeal to outside authorities or make use of special rules.
The following features of the confirmation process are intended to insure that it is unambiguous, and that neither player can use the opportunity to restart play to gain an artificial advantage:
* After two consecutive passes, the players attempt to agree on which remaining groups on the board are dead. A mechanism is suggested for this process which should work even if the players share no common language. Note that no stones are actually removed until it is clear that the players agree on the status of all groups on the board.
* Effectively, it is always the opponent of the player disputing a purportedly dead group's status who moves first when the game is restarted (although that player may choose to pass).
{{This is no longer true. The opponent of the last person to pass moves. -wjh}}
* If play is restarted, the two players must still make the same total number of moves. White always makes the very last move (or pass) of the game.
* The game ends at any point when the players agree on the status of all groups remaining on the board, or when both players pass twice in succession, in which case any stones remaining on the board are deemed alive. If necessary, White will make an additional pass at this point, passing the obligatory stone to Black, to maintain parity in the number of moves by the players. (The provision that the game must end after both players pass twice in succession is designed to prevent one player from maliciously refusing ever to agree on the status of some group, prolonging the game indefinitely.)
Points in Seki: The rules count surrounded points in seki, but not the "neutral" points (points adjacent to stones of both colors). (This allows one to score a game which is ended before all dame are filled--in fact, in principle it allows one to score any game position.)
Scoring the Game: The rules allows the use of either "area" or "territory" counting, by prior agreement. The use of pass stones and the requirement that the two players each make the same number of moves insures that the two methods will give the same result in all even games. The requirement that Black compensate White for any handicap stones given insures the same result in handicap games as well. (This could equally well have been achieved by treating White's first n-1 moves in an n-stone handicap game as passes, requiring White to pass Black n-1 pass stones. The results would then be the same, but the value of a handicap stone would then change from what we are used to; New Zealand effectively uses this system (they only count by area), but most other Chinese-style (area counting) rules seem to compensate White as we do.)
Self-Capture: Our rules make self-capture illegal. We are aware that this is more than a matter of additional ko threats, and that there are some (highly artificial) situations where the unconditional life-and-death status of a group depends on the rule on self-capture. The New Zealand Go Association allows self-capture, and some leading European players, including Matthew MacFadyen, have also suggested that allowing it might slightly enrich the game. We have chosen to stay with the traditional prohibition.
Placement of Handicap Stones: Our rules allow free placement of handicap stones, but tacitly favor the Japanese placement of handicap stones by describing it as "traditional". Clubs and tournament directors wishing to make traditional Japanese placement a requirement can easily do so.
Compensation: Our rules maintain the traditional 5 1/ 2 points of compensation.
Handling of Illegal Moves: Our rules provide that an illegal move should not automatically and immediately result in a loss. Instead, an illegal move is "punished" by being treated as a "pass"--i.e., the offending player is forced to retract the illegal move, giving the opponent a pass stone and the move. (In most serious games, this is quite severe enough!)
It is also provided that an illegal move must be noted by the opposing player before their next move. An illegal move not so noted must stand, unless the players agree to restore the game position prior to the illegal move. (These rules should be viewed in the context of AGA Tournament Regulations governing the handling of "disturbed boards", repeated or deliberate violations of the rules, etc.)
The AGA Rules Committee has asked the AGA Executive Committee to recommend, these rules to our next National Board meeting this summer, where we expect they win be ratified. {{They were. --wjh}}
* The statement of the rules must be clear, consistent, and complete. That is, they must specify unambiguously what constitutes a legal move at each stage of the game; how the end of the game is determined; how disputes over the status of groups are to be resolved; and how the game is to be scored.
* The rules must have been adopted as the official rules of at least one IGF member country or territory for some span of time to be determined by the committee. This will discourage frivolous rules proposals.
We are aware that our own "simplified" rules have not yet met the second criterion proposed here; we are not asking IGF sanction for these rules at this time. We propose to keep the IGF Rules Committee and other interested parties informed of our experiences promoting these rules in the United States, with the aim of laying the groundwork for their eventual sanction for use in international amateur play.
The AGA Rules Committee